A Shock Tube and Modeling Study about Anisole Pyrolysis Using Time-Resolved CO Absorption Measurements

Abstract

The pyrolysis of anisole (C 6 H 5 OCH 3 ) was studied behind reflected shock waves via highly sensitive absorption measurements of CO concentration using a rotational transition in the fundamental vibrational band near 4.7 µm. Time-resolved CO mole fractions were monitored in shock-heated C 6 H 5 OCH 3 /Ar mixtures between 1000 and 1270 K at 1.3-1.6 bar. The decomposition of C 6 H 5 OCH 3 proceeds exclusively via homolytic dissociation, with reaction rate k 1 , forming methyl (CH 3 ) and phenoxy (C 6 H 5 O) radicals. The subsequent decomposition of C 6 H 5 O by ring rearrangement and bond dissociation yields CO. To determine the rate constant k 2 of C 6 H 5 O decomposition avoiding secondary reactions, allyl phenyl ether (C 6 H 5 OC 3 H 5 ) was used as an alternative source for C 6 H 5 O. Its decomposition was studied between 970 and 1170 K at ß1.4 bar. The potential-energy surface of C 6 H 5 O dissociation has been reevaluated at the G4 level of theory. Rate constants determined from unimolecular rate theory are in good agreement with the present experiments. However, the obtained rates k 2 = 9.1 × 10 13 exp(−220.3 kJ mol −1 /RT)s −1 are significantly higher than those reported before (factor 6, 2, and 1.5 faster than those data reported by Lin and Lin, J. Phys. Chem. 1986, 90, 425-431;Frank et al., 1994; Carstensen and Dean, 2012, respectively). Good agreement was found between the measured CO concentration profiles and simulations based on the mechanism of Nowakowska et al. after substituting k 2 by the value obtained from experiments on C 6 H 5 OC 3 H 5 in this work. The

Reaction Mechanisms of Anisole Pyrolysis at Different Temperatures: Experimental and Theoretical Studies

“…The subsequent scission of the C–C bond (I2 → TS3 → P1) leads to a cyclopentadienyl radical and CO. The second rate-determining step has a barrier of 53.2 kcal/mol, which is consistent with previous studies. ,− Once the cyclopentadienyl radical is formed, 1,3-cyclopentadiene can be generated through recombination with H or H-abstraction from a hydrogen donor.…”

“…The reaction rate constants were measured at low to atmospheric pressures in a shock tube, 27 a stirred reactor, 28,29 and a flow reactor in the presence of hydrogen. 30 At the same time, the rate constant of the further decomposition of the phenoxy radical to form cyclopentadienyl (C 5 H 5 ) and CO was also measured 17,27,31,32 and supported with a theoretically proposed mechanism 33−35 involving formation of a bicyclic intermediate and ring opening. CH 3 , C 5 H 5 , and phenoxy radicals, which were found to be important intermediates, can recombine with an H radical or with themselves, leading to many different products.…”

“…Anisole, as the simplest aromatic model compound for the methoxy group in lignin, is not only a significant component in biomass pyrolysis oils but also has outstanding combustion properties. , Thus, to define optimal operating conditions for lignin conversion, anisole is commonly selected as a potential surrogate compound to mimic lignin pyrolysis and combustion. , Because the O–CH 3 bond is significantly weaker than other bonds in anisole, studying the anisole decomposition can provide valuable insights into the chemistry of phenoxy and cyclopentadienyl, which are important intermediates in the formation of polycyclic aromatic hydrocarbons and soot during biomass pyrolysis and combustion . In addition, as anisole has become popular as a fluorescence tracer, − the study of its thermal decomposition could help us to access the temperature and time range where it can be used in fluorescence spectroscopy . Anisole and its pyrolysis are also relevant for the food industry − and public health policies related to the flavor use in tobacco and electronic cigarette products. − …”

“…13 In addition, as anisole has become popular as a fluorescence tracer, 14−16 the study of its thermal decomposition could help us to access the temperature and time range where it can be used in fluorescence spectroscopy. 17 Anisole and its pyrolysis are also relevant for the food industry 18−20 and public health policies related to the flavor use in tobacco and electronic cigarette products. 21−23 To date, multiple studies of anisole reactivity, pyrolysis, oxidation, and combustion have been conducted with wellcontrolled experimental conditions, various state-of-the-art detection techniques, and theoretical methods, leading to determining relevant rate constants, species concentration profiles, reaction pathways, and kinetic models.…”

A Conical Intersection Influences the Ground State Rearrangement of Fulvene to Benzene

“…These reactions have been studied experimentally, both by generation of propargyl radicals and by synthesis and pyrolysis of putative intermediates. − Experiments have also been carried out on the addition of propargyl radicals to allyl radicals, HCCCH 2 + CH 2 CHCH 2 → products . For the addition of methyl radical to cyclopentadienyl, CH 3 + C 5 H 5 , the only experiments conducted so far have involved pyrolysis of anisole, C 6 H 5 OCH 3 . − These experimental studies have all been accompanied by extensive computational work on the reaction mechanisms. − …”